In general, an organic light emitting device includes two electrodes and an organic compound layer interposed between the electrodes. In the organic light emitting device, electrons and holes are injected into the organic compound layer from the two electrodes, and a current is converted into visible light. In the organic light emitting device, in order to improve performance, an electron/hole injection layer or an electron/hole transport layer may be further provided, in addition to the organic compound layer for converting the current into visible light.
However, an interface between the electrode formed of metal, metal oxides, or conductive polymers and the organic compound layer is unstable. Accordingly, heat applied from the outside, internally generated heat, or an electric field applied to the device has an adverse effect on performance of the device. Further, a driving voltage for device operation may be increased due to a difference in  conductive energy level between the electron/hole injection layer or the electron/hole transport layer and another organic compound layer adjacent thereto. Accordingly, it is important to stabilize an interface between the electron/hole injection layer or the electron/hole transport layer and another organic compound layer and to minimize an energy barrier for injection of electrons/holes from the electrode to the organic compound layer.
The organic light emitting device has been developed so as to adjust a difference of energy level between two or more electrodes and an organic compound layer interposed between the electrodes. In the organic light emitting device, an anode is adjusted to have a Fermi energy level similar to an HOMO (highest occupied molecular orbital) energy level of a hole injection layer or a material having an HOMO energy level similar to a Fermi energy level of an anode is selected for a hole injection layer. However, since the hole injection layer needs to be selected in view of an HOMO energy level of a hole transport layer or a light emitting layer close to the hole injection layer as well as in view of the Fermi energy level of the anode, there is a limitation to select a material for the hole injection layer.
Accordingly, in the method for manufacturing an organic light emitting device, a method of adjusting a Fermi energy level of an anode is adopted. However, a material for the anode is limited.
Meanwhile, it has been known that performance characteristics of a device having multi organic compound layers are affected by transport ability of charge carriers of each organic compound layer. Upon operation, resistance loss to be generated in a charge transport layer is in connection with conductivity, and conductivity has a great effect on a required operation voltage and a thermal load of the device. A band bending phenomenon occurs near a contact point between metal and the organic compound layer according to a concentration of charge carriers of the organic compound layer. With this phenomenon, charge carriers can be easily injected and contact resistance can be reduced. 